Data storage devices, and in particular, disc drives that read and write information on disc-shaped storage media, usually employ either a rotary arm actuator mechanism or a linear actuator mechanism for positioning the read/write head(s) of the disc drive over successive tracks of the disc-shaped storage medium. In most disc drives, the rotary arm or linear actuators are moved to a retracted, or parked position when the disc drive is not in use. In such a retracted position, the read/write heads of the disc drive are moved off and away from the surface(s) of the storage medium in order to prevent damage to the head(s) and storage medium. In order to resume use of the disc drive, the read/write heads must once again be loaded onto the surface(s) of the storage medium so that the data transfer can begin. It is important that the head loading operation be carried out in a controlled manner to prevent damage to the read/write heads.
Some disc drives support a head loading velocity control mechanism for a disc drive that measures the back electromotive force (BEMF) voltage across the actuator (for example a voice coil motor (VCM) actuator) of the disc drive to obtain an indication of the velocity of the actuator. The measured BEMF voltage is then employed in a control scheme to control the velocity of the actuator during a head loading operation. To perform stable velocity control, it is indispensable to accurately detect the BEMF voltage serving as velocity control information.
One existing technique to control the velocity of the VCM computes the VCM BEMF voltage based on the assumption that a VCM coil resistance is substantially constant. However, the VCM coil is subject to temperature changes and the resistance of the coil greatly changes depending on temperature. Thus, the assumption that the VCM coil resistance is constant may result in inaccurate BEMF voltage measurements and therefore improper VCM velocity control.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.